In the fabrication of semiconductor devices, metallization processes are employed to form contacts. Currently, metallization is generally achieved by providing a patterned layer of resist material and depositing a blanket layer of the desired metal. Unwanted metal is then removed by dissolving the resist and lifting off the metal in a lift-off process. Thus, these prior art techniques involve many process steps such as resist spinning, exposure, developing, cleaning and so on. All of these processes can introduce contamination, decrease yield, etc. A further problem that arises is that the structure or substrate (generally a wafer) must be removed from the growth chamber to remove the masking material. The structure is then masked again and reintroduced into the growth chamber for re-growth. Thus, the prior art techniques keep the wafer vacuum incompatible.
A second method of removing unwanted metal is etching. This requires additional masking steps. During the etching and/or mask removal processes, the material of the semiconductor device has a high likelihood of being contaminated by the etchant, which contamination greatly reduces the life of the device, the operating characteristics of the device, and the reliability of the device. Further, the etching process severely damages semiconductor material adjacent the etched areas which further reduces life, operating characteristics, and reliability. Also, etching processes are very time consuming and difficult to perform.
In addition to the etching problems, all known prior art metallization processes require many interspersed deposition, masking and etching steps which greatly complicate and lengthen the process. For example, when epitaxial layer growth and metallization steps are interspersed, the wafers must be placed in a vacuum or pressure chamber to provide the atmosphere for the growth. However, each time the wafer must be etched and/or masked, it must be removed from the chamber, resulting in large amounts of preparation time for each step. Also, each time wafers are removed from a chamber and subsequently replaced, the opening and preparation of the chamber (as well as the processing of the wafer) is an opportunity for additional impurities and contaminants to be introduced to the wafer.
Accordingly, it would be highly desirable to provide fabrication methods for semiconductor devices with improved metallization processes.
It is a purpose of the present invention to provide new and improved methods of selective metallization during semiconductor device fabrication.
It is another purpose of the present invention to provide new and improved methods of selective metallization during the fabrication of semiconductor devices which does not require removal of the substrate from the processing chamber.
It is a further purpose of the present invention to provide methods of selective metallization which can be used in combination with resistless processes.
It is still a further purpose of the present invention to provide methods of selective metallization which can be used in semiconductor diffusion processes.